Your actual award is "As of last block:".  It went up from 0.1977789BTC to 0.21367375BTC.  The "Estimated Change:" is based on what would happen if the pool found a block at that very moment.  In the 1st pic, the round has been going for 01:19:26.  You have submitted a lot of shares in that time, so you would get .00884507 BTC if the pool found a block at that very moment.  In the 2nd pic, the round has been going for 00:29:57.  At that point, you have only submitted roughly 3/8 of the shares that you submitted at the time that you took the screenshot of the previous block.  (30 minutes vs. 80 minutes)

The system is based on Proportional Payment System.  Your "Estimated Change" goes down to 0 with each new round, and goes up as you submit shares.  (Except for taking into account unpaid / shelved shares from recent blocks -- then your Estimated Change might be greater than 0 when a new round starts.)  Your overall Shares Rewarded is at 98.75%, which is pretty high, so you don't have very many shelved shares to pay out.

Every round, while the round has >100% luck, for every 10 minutes of hashes your "Estimated Change" should be a little more than +.001 BTC.  Once the round drops below 100% luck, this number will decrease.